The present invention is directed to multicast delivery systems and methods, and more specifically, to systems and methods for efficient and effective multicast delivery over hub and spoke networks, including satellite-based hub and spoke networks.
Reliable data delivery over computer networks traditionally relies on unicast data transfers, which establish point-to-point connections between devices. In situations where the same data is transferred to multiple users, the server sends a copy of the file to each recipient independently. The unicast delivery of the same content to a number of remote sites is both time consuming and wasteful of bandwidth resources. A simplified example is shown in FIG. 1, which indicates a sender station 10 establishes individual TCP connections 12–18 with an N number of end stations 20. As shown, sender station 10 establishes a unicast connection with each end station 20.
An alternative to establishing a unicast connection for each end station involves the use of multicast technology. Multicast technology transmits a single data stream to multiple recipients. However, multicast capability built into the internet protocol (IP) is typically a user datagram protocol (UDP) based, best effort service. This service tends to be unreliable, and is typically appropriate only for real-time streaming applications such as video conferencing and event broadcasting. Further, UDP-based IP multicast does not include mechanisms for the detection and retransmission of lost or corrupted data, or the resequencing of packets that arrive at the receiver out of order. For at least these reasons, IP multicast is typically ill suited for file downloads and other data transfer applications.
Attempts to overcome the problems inherent in unreliable UDP-based multicast transmission include the use of forward error correction applications that attempt to increase the probability that all the data will arrive at each receiver. However, such applications require additional bandwidth utilization. Further, the applications require the loading of software onto each device that will act as a multicast sender or receiver. Additional problems with current multicast options also exist, which hinder their use with common TCP applications.
Similar problems for satellite-based, hub and spoke networks exist for multicast distribution. However, certain features of satellite-based networks make them particularly well-suited for using multicast services. Such satellite-based networks typically attempt data delivery using a broadcast mechanism, such as digital video broadcast (DVB). As a result, every data packet is automatically transmitted from the hub to every spoke or remote receiver site, whether the packet is destined for that remote site or not. This makes such satellite-based networks useful for multicast data services because all remote sites receive every packet. Hence, it would be desirable to make use of these attributes while simultaneously making improvements over the current state of unicast and multicast transmissions.